Cells for studying the capacity of a system consisting of liquid and gas to form gas hydrates are known. In laboratory installations, pilot and/or industrial plants, gas hydrate formation is detected either by a temperature increase because crystallization is exothermic, or, when the working device is respectively closed or semi-closed (allowing the pressure to be maintained), by a pressure drop or by a sudden gas consumption. It is also possible to detect hydrate formation by visual examination. It should be emphasized that, in most of these methods, it is necessary to form (or to dissociate) a large number of hydrate crystals to obtain a significant signal. In the case of gas systems with low water contents, equilibrium cells with water content measurement by gas chromatography or coulometry are used.
Gas hydrates are crystals comprised of a network of water molecules stabilized by hydrate formers (such as CO2, H2S, nitrogen, . . . ). Gas hydrates form under high pressure and low temperature conditions. If these crystals form, they grow, agglomerate and eventually clog pipes. Clogging remediation is long, difficult and dangerous. Currently, operators implement extensive and costly technical solutions to prevent formation of such crystals.
One object of the present invention is to provide a simplified device enabling early detection and measurement of gas hydrate formation, thus allowing implementation of effective remediation techniques for hydrate formation.
Raman spectrometry is a non-destructive and non-invasive technique for studying molecular bond vibrations that is currently commonly used for investigating the structure and the composition of natural or synthetic gas hydrates. Indeed, it is known that, in case of pure gas hydrates, Raman spectrometry allows to identify, through the vibration modes of the host molecules, the structure of the gas hydrate (of SI, SII or SH type) and to quantitatively determine the relative occupancies of the various cavity types of these different hydrate crystals. In the case of mixed hydrates (stabilized by a gas mixture), the technique allows to qualitatively identify the structure of the hydrate formed and the nature of the host molecules.
Raman spectrometry has already been used as a means of studying solid water formation.
The present invention is based on the fact that using Raman spectra in the vibration mode zone of the OH bonds of a water-containing medium likely to form solid crystals (such as ice and/or hydrates) allows, with the combination of a temperature measurement, to identify the presence or not of crystals by using a simplified measuring device.